Important characteristics of an effective commercial assay include specificity, sensitivity, a high multiplexing capacity, and the ability to perform the assay rapidly and in a cost-effective manner, preferably through automation. For nucleic acid assays, many strategies have been designed to improve sensitivity that involve amplification of either the target sequence, e.g. polymerase chain reaction (PRC), or amplification of the signal generated from a recognition event, e.g. Invader® assay, U.S. Pat. No. 5,846,717. In contrast, for non-nucleic acid analytes, the option of target amplification is generally not available; thus, increases in sensitivity are brought about by signal amplification, e.g. enzyme-linked immunoabsorbent assays (ELISAs), Malik et al, Editors, Antibody Techniques (Academic Press, New York, 1994); tryamide signal amplification (TSA), Bobrow et al, J. Immunol. Methods, 125: 279-285 (1989); and the like.
In spite of the tremendous progress that has been made in recent years toward the developing highly sensitive and robust assay systems, few if any of the current technologies combine high sensitivity, specificity, and facile multiplexing capability. As a result, in some applications, such as certain drug screening or toxicological studies where samples are scarce, one has only a very limited ability to measure multiple analytes in individual samples.
In view of the above, it would be advantageous to many fields, particularly the fields of life science and pharmaceutical research, to have available a broadly applicable, specific, and sensitive assay technique that can be readily adapted for measuring multiple analytes in a single sample.